Approximate Cache Control With Mapping Validity Feedback
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Solution Overview
Problem
Approximate caching reduces query response time but introduces errors due to the lack of proper error control in mapping input queries to output values.
Innovation Solution
A controller for a cache that stores input queries as approximate inputs with associated state information to monitor the validity of mappings, reducing errors by verifying and correcting mappings when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If approximate caching is used to reduce query response time, then query response time is improved, but mapping errors are introduced
Solution Approach 1:
The system implements feedback mechanisms through query counters and validation flags that track the accuracy of approximate cache mappings. When the query counter reaches a threshold or validation fails, the system retrieves the correct output from the computation unit to verify and update the cache entry, ensuring mapping accuracy while maintaining fast cache retrieval for valid entries
Solution Approach 2:
The system performs preliminary validation by setting validation flags and establishing query thresholds before cache entries are fully trusted. This preliminary action prevents erroneous mappings from propagating errors while still allowing the cache to function quickly for validated entries
2Reliability
If state information is added to monitor mapping validity, then mapping accuracy is improved, but device complexity increases
Solution Approach 1:
The state information structures serve multiple functions: query counters both limit cache usage and validate mapping accuracy, while validation flags both track errors and control retrieval behavior. This multi-functionality reduces the need for separate monitoring mechanisms, thereby limiting complexity increase while improving reliability
3Reliability
If cache entries are validated and corrected, then mapping accuracy is improved, but query processing time increases
Solution Approach 1:
The system applies validation and correction only partially - only when query counters reach thresholds or validation flags indicate potential errors. For the majority of cache hits with valid state information, the system retrieves results immediately without full validation, thus maintaining fast query processing while still improving mapping accuracy for uncertain entries
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(b)
AI summary
The present invention relates to a controller (1) for a cache (2). The cache (2) is configured to store one or more outputs of a computation unit (3). The controller (1) is configured to map input queries to one or more approximate inputs. For each of the one or more approximate inputs, the controller (1) is configured to store, in the cache (2), the approximate input (h) in association with a respective output (y) of the one or more outputs and a respective state information (SI) as a cache entry (2a). The respective state information (SI) comprises information for monitoring validity of a mapping of the approximate input (h) to the respective output (y) of the cache entry (2a). Moreover, the present invention relates to a system comprising such a controller and a cache as well as to a method for controlling a cache.